If you study essential oil monographs and aromatic plant profiles, you will find some common botanical terms used in the “plant description” section. However, unless you are familiar with these terms, they might be confusing. Here are five common botanical terms that are often used to describe the life span and behavior of an aromatic plant: Annual, biennial, perennial, evergreen, and deciduous.
Annual Aromatic Plants
Annual aromatic plants usually survive for just one growing season; in the botanical world this usually means spring and summer. A true aromatic annual will grow from seed to plant, bloom and die within the space of one season. The seeds produced by the dying plant will start the life cycle of a new plant in the following season but the original plant will not return to life. However, depending upon your climate, you might be able to squeeze more than one growing season out of an annual plant. I have managed to extend the life of several annual plants to another growing season by overwintering the plant indoors and protecting it from cold and freezing temperatures. Some plants have this capability (depending upon the growing climate) which is why you may see some plants described as annual, biennial, or perennial in the “plant description” section; an example of such a plant is sweet marjoram(Origanum marjorana). Examples of other annual plants used in aromatherapy include sunflower(Helianthus annuus), dill* (Anethum graveolens), and basil (Ocimum basilicum).
Biennial Aromatic Plants
A biennial aromatic plant will normally take two growing seasons to complete its life cycle. During the first season, the plant will produce basic structures, such as roots, leaves and stems; during the second season, the plant will produce flowers, fruit, and seeds before it dies. In the period between the first and second growing season (usually in the winter months), the plant will be dormant. Biennial plants usually have a lifespan of two years. Biennial aromatic plants include parsley (Petroselinum sativum), clary sage (Salvia sclarea)*, and fennel (Foeniculum vulgare)*.
Perennial Aromatic Plants
Perennial aromatic plants live for more than two years and through several growing seasons. The part of the perennial plant that is above ground usually dies back each year but the part of the plant that is below ground (i.e. the roots) regrows the following season to produce leaves and blooms. Some perennial plants may keep their foliage throughout the winter season, too. Examples of aromatic perennial plants include peppemint (Mentha x piperita), lavender (Lavandula angustifolia), rosemary (Rosmarinus officinalis), and geranium (Pelargonium graveolens).
Evergreen Aromatic Plants
Evergreen is a botanical term used to describe the behavior of a plant, in terms of its leaf coverage. A plant that is evergreen will maintain its leaves through all of the seasons. There are various types of evergreen plants from conifer trees to tropical rain forest plants. Examples of aromatic evergreen species include cedarwood (Cedrus atlantica), clove (Syzygium aromaticum), orange (Citrus aurantium var. amara), and Scotch pine (Pinus sylvestris).
Deciduous Aromatic Plants
Deciduous aromatic plants lose their leaves after the end of the growing season; in the northern hemisphere, this usually occurs in the colder months such as Fall and winter. However, in more tropical climates, deciduous plants usually lose their leaves during the dry season, or when rainfall is sparse. Examples of deciduous plants used in aromatherapy include lime blossom (Tilia europea), walnut (Juglans regia), and some species of Eucalyptus.
Further Definition of Plant Description Terms
Some plants are semi-evergreen or semi-deciduous. Some plants are both annuals and perennials, depending on their growing location. Some plants are also evergreen perennials or deciduous perennials. In summary, it is not easy deciphering the world of aromatic plants! Learn the most commonly used terms, and apply them to your aromatherapy learning.
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Capon, Brian, Botany for Gardeners, 3rd Edition, 2010, US: Timber Press
Author is a UK-certified aromatherapist, published author in aromatherapy, an approved education provider for the National Association for Holistic Aromatherapy (NAHA), an aromatherapy business owner, and Chief Editor for the NAHA Aromatherapy Journal.